Apparatus and method for automatic correction of pole-zero error in a spectroscopy system

ABSTRACT

A spectroscopy system is provided having an automatic pole-zero error correction circuit. A gated integrator of the system integrates a shaped pulse and trailing edge of the shaped pulse for sampling by an analog-to-digital converter. A pair of samples are converted along the slope of each integrated shaped pulse passing through the system. The two samples are compared on a pulse by pulse basis. An algorithm generates a control word for affecting a change in a pole-zero network coupled along a shaping amplifier of the system. In response to the control word, an MDAC of the pole-zero network affects a change in the system to correct the pole-zero error. When the pole-zero error is eliminated or reaches an acceptable user level, the correction circuitry automatically shuts off.

PRIOR APPLICATIONS

This application is a §371 U.S. National Phase application which basespriority on International Application No. PCT/US99/21791, filed Sep. 3,1999.

GOVERNMENT LICENSE RIGHTS

This invention was made with U.S. Government support under contract orgrant DASG60-96-1-0005 awarded by U.S. Army Space and Missile DefenseCommand. The U.S. Government has certain rights in the invention.

TECHNICAL FIELD

This invention relates to a pole-zero error correction circuit. Moreparticularly, it relates to an automatic pole-zero error correctioncircuit for use in an ionizing radiation spectroscopy system.

BACKGROUND ART

Spectroscopy systems are used for the measurement and analysis ofelectromagnetic spectra arising from the emission or absorption ofradiant energy. Most radiation spectroscopy systems employ a radiationdetector for receiving incident radiation so that a charge, proportionalto the incident radiation energy, can be provided. This charge isdirected to a charge sensitive preamplifier for forming a voltage pulseexhibiting a fast rise time with a long decay time typically on theorder of 5 us-1000 us. Further analog amplification and filtering areperformed upon this pulse to provide a properly amplitude scaled pulsewith good signal-to-noise characteristics. The filtering, also known aspulse shaping, is typically implemented in the form of active high passor differentiation filter stages followed by several active low passfilter stages. Collectively, the various stages could be called a pulseshaping network. A typical pulse shaping network forms a pulse having asemi-Guassian shape—one which resembles a bell.

Optimal performance of a spectroscopy system is best realized when theoutput of the pulse shaping network returns to baseline withoutextending for a long period of time above or below the baseline. If theoutput pulse of the pulse shaping network fails to return to baseline,an error is introduced into the system during the measurement of thenext pulse which occur randomly in time and amplitude. The differencebetween the time constants of the preamplifier and high-pass filterstages of the spectroscopy system is the source of the error. Adjustmentin the pulse shaping network by some type of pole-zero adjustment meansis required to correct this error.

Some correction circuits have been introduced into spectroscopy systemswhich permit manual adjustment of the error. The device of U.S. Pat. No.4,491,799 to Giardinelli is used with a manual adjustment system andpermits the operator to verify that the proper manual adjustment hasbeen made. In particular, the Giardinelli device employs a pair of LEDsfor providing a visual indication of the value and polarity of a boxcarintegrator output. If one of the LEDs illuminates, the operator knowsthat the baseline has either fallen below or has remained above thepreferred null point. Manual adjustment is then implemented until bothLEDs fail to illuminate indicating that the baseline is at the desirednull point. The Giardinelli invention attempts to eliminate the need forreading an oscilloscope, but falls short of providing a system which canprovide accurate, let alone automatic pole-zero cancellation. Inparticular, the Giardinelli invention is a completely analog circuitcontaining many inherent qualities which contribute to the exact errorin which the invention is attempting to eliminate (i.e., phase shifts,time phase anomalies, temperature drifts and component tolerances).Further, there exists no means for calibrating the circuit to compensatefor the error introduced by the circuit. Still further, the Giardinellicircuit uses a boxcar integrator for sampling the baseline of each pulsepassing through the circuit and for providing an average value for thebaseline based on all of the sampled pulses. But, since pulses arerandom in nature, in time and frequency, sample averaging is at best anapproximation of the conditions passing through the circuit and do notrepresent truly ideal conditions needed for an accurate spectroscopysystem. Essentially, low count scenarios will result in inaccurateresults when using the Giardinelli device. Yet still further, theGiardinelli device requires an operator to make a manual adjustment,through the use of a potentiometer, to achieve proper compensation.Operator error also contributes to inaccurate results.

U.S. Pat. No. 4,866,400 to Britton et al. discloses an automaticpole-zero adjustment circuit for use in ionizing radiation spectroscopysystems and represents an improvement over circuits then known in theprior art such as the Giardinelli device. However, as will be discussed,the invention shown therein still fails to provide a pole-zerocancellation circuit which can accomplish its function without the useof un-needed additional components, as well as being a circuit whichrelies on pulse sample averaging for determining whether the baselinehas returned to the desired null point. The Britton device uses ananalog averager to form an average value of the over or under-shoot of aplurality of pulses. Thereafter, the ADC samples this averaged value.Once a plurality of pulses have passed therethrough, the valuerepresenting the average amplitude, outputted from the ADC, is directedto a control circuit which affects a command upon a pole-zero networkcoupled to the system. Unfortunately, such as discussed in Giardinelli,sample averaging is inherently deficient in that it does not representtrue real time dynamic sampling. Britton also uses the additionalanalog-to-digital converter (above what is normally needed in aspectroscopy system) with the boxcar averager in its control circuitry,thereby dissipating additional power, as well as adding further cost andcomplexity to the circuit. Further, the Britton control circuitry isrelying on a single average value of the sampled pulses and is notconfigured to accept and process continuous individual values passingthrough its circuitry. Accordingly, it is configured only to output asingle control word in response to a single accepted sampled value.

An improved pole-zero error correction device/circuit is needed for usein ionizing radiation spectroscopy systems which can overcome thedeficiencies in the prior art. The improved device should eliminateanalog averaging and rely on the actual value of each sampled pulse (apulse-by-pulse basis) for determining the extent of the pole-zero error.Further, the device should eliminate un-needed components which tend todissipate additional power and impose additional cost and complexity tothe system. Finally, the improved pole-zero device should automaticallycorrect the error and then shutdown once the error has been corrected.

DISCLOSURE OF INVENTION

We have invented an improved pole-zero error correction circuit andmethod for correcting pole-zero error in an ionizing radiationspectroscopy system. Our circuit overcomes the deficiencies seen in theprior art and represents a major improvement to that which is known bythose skilled in the art.

An automatic pole-zero error correction circuit couples to an ionizingradiation spectroscopy system. The circuit includes a pole-zero networkcoupled to the spectroscopy system as part of a larger feedback controlsystem. The pole-zero network has a characteristic which varies inresponse to an input control signal received from a pole-zerocompensation circuit. The pole-zero network performs an adjustment tothe spectroscopy system to correct the pole-zero error within thespectroscopy system. A gated integrator extends the shaped pulses for aset duration permitting two samples to be converted by ananalog-to-digital converter (ADC) along the slope of each integratedpulse passing through the spectroscopy system. The two conversionresults taken from each pulse are directed to the pole-zero compensationcircuit for generation of an appropriate correction signal forsubsequent injection upon the pole-zero network. The correction signalis a digital algorithm representing a digital correction factoroutputted from a digital controller of the pole-zero compensationcircuit.

The novel approach of correcting pole-zero error within a spectroscopysystems, as seen herein, provides a much higher degree of accuracy forcorrection of the pole-zero error over those circuits, devices andmethods known in the prior art. In particular, the present device canachieve superior results over those devices utilizing boxcar averaging,a method of analog sampling known to be susceptible to errors especiallywhen the repetition rate of the pulses is low. Further, the device ofthe present invention, taking two samples along the trailing edge of theextended pulse waveform, is actually measuring the area of the pulse andnot the amplitude, a method of measuring for pole-zero error not seenhereto before. The device of the present invention also utilizes areduced component count which dissipates less power, saves space andreduces cost of manufacturing. Reduced component count, as compared tothose systems in the prior art, is realized through the novel use ofcomponents already provided in the spectroscopy system.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be best understood by those having ordinary skill inthe art by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a first prior art spectroscopy systemcapable of affecting manual pole-zero error correction;

FIG. 2 is a block diagram of a second prior art spectroscopy system,similar to that of FIG. 1, capable of affecting automatic pole-zeroerror correction through the use of added circuitry;

FIG. 3 is a block diagram of a novel spectroscopy system of the presentinvention capable of affecting automatic pole-zero error correctionwithout the need for additional control circuitry;

FIG. 4 is a schematic diagram of the circuitry used in the pole-zeronetwork of the novel spectroscopy system of the present invention;

FIG. 5 is a schematic diagram of the circuitry used in the gatedintegrator of the novel spectroscopy system of the present invention;

FIG. 6 is a flow diagram of a simple correction implementation carriedout by the novel spectroscopy system of the present invention utilizingeither a field programmable gate array or a firmware controlledmicroprocessor;

FIG. 7 is a flow diagram of a proportional correction implementationcarried out by the novel spectroscopy system of the present inventionutilizing a firmware controlled microprocessor;

FIG. 8 is a flow diagram of a binary search routine which can be usedwith the novel spectroscopy system of the present invention to determineand correct the pole-zero error;

FIG. 9 is a representation of an oscilloscope output depicting a pulsewith over-compensated pole-zero cancellation;

FIG. 10 is a representation of an oscilloscope output depicting a pulsewith under-compensated pole-zero cancellation; and

FIG. 11 is a representation of an oscilloscope output depicting a pulsewith correct pole-zero cancellation.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a first prior art spectroscopy system is shown. Thefirst prior art system employs a peak hold stage coupled directly to ananalog-to-digital converter (ADC) stage for measuring the amplitude of ashaped pulse passing through the system. By using a display apparatus,such as an oscilloscope or a pair of LEDs (as in the Giardinellireference), a determination can then be made whether any pole-zero errorexists in the system. Thereafter, manual adjustment can be made to thesystem through manipulation of the pole-zero network coupled to thesystem. Manual adjustment in this first prior art system could beaffected by a potentiometer, for example.

Referring to FIG. 2, a second prior art spectroscopy system is shown.The second prior art system employs similar components as in the firstprior art system with the addition of an analog boxcar averager, ansecond ADC and a control circuit. These additional components arecoupled to this second prior art system for affecting an automaticpole-zero error correction. However, these components add complexity andcost to the system, require additional space within the system anddissipate additional power.

Referring to FIG. 3, a novel spectroscopy system of the presentinvention is shown. The novel system employs a dual purpose gatedintegrator. Purpose number 1 replaces the peak hold circuit of the twoprior art systems shown in FIGS. 1 and 2 respectively. Accordingly,purpose number 1 for the gated integrator, used in conjunction with anADC, measures the area of the shaped pulses passing through the system.Purpose number 2, a use not seen in the prior art, assists in measuringthe extent of the pole-zero error. This is accomplished by extending theoutput waveform emanating from the gated integrator for subsequentsampling by the ADC. The ADC coupled to the gated integrator samples theextended waveform slope twice. Depending on whether the value of thefirst sample is greater or less than the value of the second sample, analgorithm, generated by a digital controller located within the digitalcontrol & display stage, is applied to the pole-zero network forcancellation of the pole-zero error.

Referring to FIG. 4, a pole-zero network, employed in the novelspectroscopy system of the present invention is shown. The pole-zeronetwork contains, inter alia, a multiplying digital-to-analog converter(MDAC). The MDAC receives a “PZ Control Word” (see FIG. 4) which isgenerated by an algorithm. Referring to FIG. 3, the pole-zero networkshown in FIG. 4 is coupled to the spectroscopy system along a high-passshaping network between the preamplifier and low-pass shaping networkstages.

Referring to FIG. 5, a schematic diagram is shown depicting thecircuitry used in the gated integrator of the novel spectroscopy systemof the present invention. Accordingly, the resistor R1, capacitor C1,op-amp and switch shown in FIG. 5 is included in the box labeled “gatedintegrator” on FIG. 3.

In a preferred method of operation, the pole-zero cancellation procedurefollows “simple implementation” wherein the PZ Control Word directs thepole-zero network to increment or decrement, depending on any differencein voltage level of the two samples, by a value of 1. In an alternatemethod of operation, the pole-zero cancellation procedure follows“proportional integral implementation” wherein the PZ Control Worddirects the pole-zero network to increment or decrement, again dependingon any difference in voltage level of the two samples, by a varyingvalue proportional to the amount of difference between the two samples.This procedure is based on PID or “proportional integral derivative.” Inyet another method of operation, a “binary search implementation” can beemployed for reducing the number of samples needed to correct thepole-zero error to an acceptable level. Each of the above threeimplementation procedures will be more fully discussed laterhereinafter, with reference to FIGS. 6-8.

Regardless of the implementation procedure used, and so long as thepole-zero correction circuitry is activated, the novel system of FIG. 3measures the pole-zero error then occurring in the spectroscopy systemafter each pulse. Accordingly, new PZ Control Words are constantly beinggenerated by the digital controller and directed to the pole-zeronetwork after each pulse. The novel system of FIG. 3 will continue togenerate PZ Control Words until the pole-zero error is eliminated (i.e.,the value of the two samples are equal). Thereafter, the pole-zero errorcancellation circuitry automatically shut-downs.

Referring to FIGS. 9-11, oscilloscope display representations aredepicted showing waveforms relating to pole-zero error. The broken linein all three figures represents the proper baseline. FIG. 9 representsan over-compensated pole-zero canceled waveform. Hence, if two samplesare taken along the trailing edge of the semi-Gaussian shaped pulse (theupper waveform), the second sample would have a lesser value than thefirst sample (i.e., the baseline is positive). FIG. 10 represents anunder-compensated pole-zero canceled waveform. Here, if two samples aretaken along the trailing edge of the semi-Gaussian shaped pulse, thesecond sample would have a greater value than the first sample (i.e.,the baseline is negative). FIG. 11 represents a properly compensatedpole-zero canceled waveform. Here, if two samples are taken along thetrailing edge of the semi-Gaussian shaped pulse, the second sample wouldhave an equal value with that of the first sample (i.e., the baselinehas returned to the proper level).

Various novel methods of implementing the pole-zero cancellationprocedure can be used with the system of the present invention shown inFIG. 3. Three such methods are shown in FIGS. 6-8, respectivelyrepresenting: simple implementation, proportional integralimplementation and binary search implementation.

As shown in FIG. 6, a preferred method of operation is illustratedwherein simple implementation is used to perform the pole-zerocancellation procedure in a spectroscopy system. The logic of thismethod can be affected by an FPGA (field programmable gated array) orpreferably by firmware stored in a microprocessor. In either form, themethod is followed in the same manner. In particular, a first sample isread in from the ADC and designated as A1. A short delay of about 5 usis then timed out to allow for the first sample to fully convert. Thistime delay can be extended to allow for a more accurate reading of theintegrator slope if desired. After the delay, a second sample is read infrom the ADC and is designated as A2. A query is then made askingwhether A1 is less than A2 (A1<A2 ?). If the answer is no, another queryis made asking whether A1 is greater than A2 (A1>A2 ?). However, if theanswer to “A1<A2 ?” is yes, a different query is made asking whether theDAC equals zero (DAC=0 ?), wherein the DAC is the current PZ ControlWord setting (a numeric value between a range dependent upon the bitvalue of the MDAC, such as, for example, 0-4095 for 12 bit, 0-65535 for16 bit or 0-1048575 for 20 bit wherein the mathematical equation of2^(n)−1 determines the maximum value and n equals the number of bits).If the answer is yes (DAC=0), then the procedure stops since the PZControl Word can not be decremented below the value of zero—its minimumvalue. However, if the answer to “DAC=0 ?” is no, then a new DAC valueis set by decrementing the current DAC by one which is expressed byDAC=DAC−1. The MDAC is then updated with the new DAC value. Thereafter,the new DAC value is directed to the beginning of the algorithm forfurther processing of the next pulse. Returning to an earlier portion ofthis simple implementation procedure wherein the answer to “A1<A2 ?” wasno, it was stated that a second query is made asking whether A1 isgreater than A2 (A1>A2 ?). If the answer to this query is no, then theprocedure enters a stop sub-procedure (to be discussed hereinafter).However, if the answer to “A1>A2 ?” is yes, then a query is made askingwhether the DAC equals 4095 (DAC=4095 ?), wherein again the DAC is thecurrent PZ Control Word setting (the value of 4095 is used in thepreferred embodiment since a 12 bit MDAC is being used). If the answerto “DAC=4095 ?” is yes, then the procedure stops since the PZ ControlWord can not be incremented above the value of 4095—its maximum value.However, if the answer to “DAC=4095 ?” is no, then a new DAC value isset by incrementing the current DAC by one which is expressed byDAC=DAC+1. The MDAC is then updated with the new DAC value. Thereafter,the new DAC value is directed to the beginning of the algorithm forfurther processing of the next pulse.

With continuing reference to FIG. 6, a stop sub-routine is implementedif the answer to the query “A1>A2 ?” is no. As shown in FIG. 6, thispresumes that the answer to the query is “A1<A2 ?” is also no. In otherwords, A1 must equal A2 (the desired result of this simpleimplementation procedure for cancellation of the pole-zero error).However, the stop sub-procedure does not merely take one reading andthen stop. Within the stop sub-procedure, a query is made asking whetherthe stop criteria has been met. If the answer is yes, then the proceduredoes in fact stop and no more incrementing or decrementing occurs. But,if the answer is no, then the value of the DAC is redirected to thebeginning of the algorithm for additional processing. The definition ofthe stop criteria in the preferred embodiment is whether the last fivepulses have resulted in A1=A2 (although the amount of pulses to checkcan be set to any desired number). Additional variations on the stopcriteria include testing the average of the last five pulse two sampledifferences or verifying that the differences in two samples of eachpulse of a series of pulses fluctuate by a very small degree. If thestop criteria has been met (the answer is yes), then procedures leads toan actual stop. The stop sub-routine ensures that a series of pulsespassing through the system are consistently yielding equal or nearlyequal values for the two samples before the correction circuitry is shutoff.

With reference to FIG. 7, a proportional integral implementation methodis shown for canceling pole-zero error in a spectroscopy system. In suchmethod, a proportional calculation and an integral calculation aresimultaneously performed and thereafter summed for establishing a valuewhich is compared to an “acceptable error band” value. If this summedvalue is less than the acceptable error band, the procedure stops. Ifnot, the DAC is decremented by the summed value and redirected to thebeginning of the procedure for further processing. In particular, apulse is received, sampled a first time by the ADC, read into theproportional integral procedure and given a value represented by A1. Ashort delay of about 5 us is again timed out to allow for the firstsample to fully convert. This time delay could also be extended to allowfor a more accurate reading of the integrator slope if desired, just asin the simple implementation. Next, a second sample from the same pulseconverted by the ADC is read and given a value represented by A2. D1,the difference in the two samples of the current pulse, is thencalculated (D1=A2−A1). At this point, two different pathways arefollowed—a first pathway calculates an integral value I (a history ofthe difference) while a second pathway calculates an proportional valueP (the current difference). In the integral pathway, S is firstcalculated by summing D1, D2 and Dn (D1+D2+ . . . Dn) where n equalssome finite predetermined number. In the preferred embodiment, n equalssix. Thereafter, I is calculated by multiplying S with ai, wherein ai isa predetermined integral gain constant. At the same time, P iscalculated by multiplying D1 with ap, wherein ap is a predeterminedproportional gain constant and D1 is the difference between the twosamples of the current pulse. The two gain constants, ai and ap, areempirically determined, their values based on the MDAC circuit andshaping times employed within the spectroscopy system). Next, E iscalculated by summing I and P. The value of E is then compared to Bwherein B represents the acceptable error band. A query is made askingwhether E is less than B (E<B ?). If the answer is yes, then theprocedure stops since E is below the acceptable pole-zero error level.However, if the answer is no, then a new DAC value is calculated bysubtracting the value of E from the existing DAC value. The MDAC is thenupdated with the new DAC value. Thereafter, the new DAC value isdirected to the beginning of the algorithm for further processing of thenext pulse.

Referring to FIG. 8, a binary search implementation is shown forperforming pole-zero cancellation in a spectroscopy system of thepresent invention. In such procedure, a DAC and ADJUST value are firstset according to numeric values relative to the bit value of the MDACused in the circuit. As noted above, the preferred embodiment uses a 12bit MDAC. Therefore, the DAC value is set at 2048 (or half of themaximum value) and the ADJUST value is set to 1024 (or half of thepreset DAC value). When a pulse passes through the system, a firstsample is taken and represented by A1. A short delay of about 5 us istimed out to again allow for the sample to fully convert. As with theother two implementations, this time delay can be extended to provide amore accurate reading of the gated integrator slope. Thereafter, asecond sample is taken and represented by A2. Next, A1 and A2 arecompared to determine whether A1 is less than greater than or equal toA2. If A1 is equal to A2, then the stop sub-routine is implemented (justas in the simple implementation). If A1 is less than A2 (A1<A2 ?), thena new DAC value is calculated by decrementing the current DAC value bythe ADJUST value. If A1 is greater than A2 (A1>A2 ?), then a new DACvalue is also calculated, but is instead calculated by incrementing thecurrent DAC value by ADJUST value. Regardless of which path is chosen,subsequent to the calculation of the new DAC value, a query is madeasking whether the ADJUST value equals 1—the minimum value for theADJUST. If the answer is yes, then the new DAC value and ADJUST value of1 are directed to the beginning of the procedure for further processing.However, if the answer to “ADJUST=1?” is no, then a new ADJUST value iscalculated by dividing the current ADJUST value by 2. Thereafter, thisnew ADJUST value and the new DAC value are directed to the beginning ofthe procedure for further processing.

Equivalent elements can be substituted for ones set forth above toachieve the same results in the same manner and way. Further, equivalentsteps can be substituted for the ones set forth above in theimplementation procedures to practice the same method in the manner andthereby achieve the same results.

What is claimed is:
 1. An automatic pole-zero error correction circuitfor use in an ionizing radiation spectroscopy system having apreamplifier and a high-pass and low-pass shaping network for generatinga shaped pulse, the automatic pole-zero error correction circuitcomprising: a) a pole-zero network coupled to the ionizing radiationspectroscopy system along the high-pass shaping network between thepreamplifier and low-pass shaping network, b) a gated integrator coupledto the low-pass shaping network for integrating the shaped pulse and atrailing edge of the shaped pulse forming a signal having a slopeproportional to the pole-zero error in the ionizing radiationspectroscopy system, c) an analog-to-digital convertor (ADC) coupled tothe gated integrator for converting two samples along the slope of theintegrated shaped pulse, d) a digital control circuit coupled to the ADCfor receiving the two samples converted by the ADC, for comparing thevalues of the two samples to each other, for generating a control signalin response to the two sample value comparison and for applying thecontrol signal to the pole-zero network, and e) the pole-zero networkaffecting pole-zero error correction upon the ionizing radiationspectroscopy system in response to receiving the control signalsgenerated and applied by the digital control circuit.
 2. The automaticpole-zero error correction circuit of claim 1, wherein the pole-zeronetwork includes a multiplying digital-to-analog converter (MDAC) forreceiving the digital control circuit control signal, for storing anumeric value and for affecting the pole-zero error within the ionizingradiation spectroscopy system.
 3. The automatic pole-zero errorcorrection circuit of claim 2, wherein the MDAC of the pole-zero networkstores a numeric value taken from a numeric value range dependent on abit-value of the MDAC.
 4. The automatic pole-zero error correctioncircuit of claim 2, wherein the MDAC numeric value is incremented ordecremented by a numeric value of one in response to receiving thecontrol signal.
 5. The automatic pole-zero error correction circuit ofclaim 2, wherein the MDAC numeric value is incremented or decremented byan integer value equal to or greater than two in response to receivingthe digital control circuit control signal.
 6. The automatic pole-zeroerror correction circuit of claim 1, wherein the digital control circuitemploys digital programmable logic.
 7. The automatic pole-zero errorcorrection circuit of claim 1, wherein the digital control circuitemploys either a microcontroller or a microprocessor.
 8. Anautomatically correcting pole-zero error ionizing radiation spectroscopysystem comprising: a) a radiation detector providing a chargeproportional to energy absorbed from incident radiation subjected to theradiation detector, b) a charge sensitive preamplifier coupled to theradiation detector forming a voltage pulse, c) a shaping amplifiercoupled to the charge sensitive preamplifier having high-pass andlow-pass filtering networks forming a shaped pulse from the voltagepulse outputted from the charge sensitive preamplifier, d) a pole-zeronetwork coupled along the shaping amplifier affecting pole-zero errorcorrection upon the automatically correcting pole-zero error ionizingradiation spectroscopy system in response to a control signal receivedfrom a digital control circuit of the system, e) a gated integratorcoupled to the shaping amplifier for integrating the shaped pulse and atrailing edge of the shaped pulse forming a signal having a slopeproportional to the pole-zero error in the automatically correctingpole-zero error ionizing radiation spectroscopy system, f) ananalog-to-digital convertor (ADC) coupled to the gated integrator forconverting two samples along the slope of the integrated shaped pulse,and g) the digital control circuit coupled to the ADC for receiving thetwo samples converted by the ADC, for comparing the values of the twosamples to each other, for generating the control signal in response tothe two sample value comparison and for applying the control signal tothe pole-zero network.
 9. The ionizing radiation spectroscopy system ofclaim 8, wherein the pole-zero network includes a multiplyingdigital-to-analog converter (MDAC) for receiving the digital controlcircuit control signal, for storing a numeric value and for affectingthe pole-zero error correction within the ionizing radiationspectroscopy system.
 10. The ionizing radiation spectroscopy system ofclaim 9, wherein the MDAC of the pole-zero network stores a numericvalue taken from a numeric value range dependent on a bit-value of theMDAC.
 11. The ionizing radiation spectroscopy system of claim 9, whereinthe MDAC numeric value is incremented or decremented by an integer valueequal to or greater than one in response to receiving the controlsignal.
 12. The ionizing radiation spectroscopy system of claim 8,wherein the digital control circuit employs circuitry chosen from thegroup consisting of digital programmable logic, a microcontroller and amicroprocessor.
 13. A method of correcting pole-zero error in aspectroscopy system, the spectroscopy system having pole-zero errorcorrection circuitry including a radiation detector coupled to a chargesensitive preamplifier coupled to a shaping amplifier coupled to a gatedintegrator coupled to an analog-to-digital converter (ADC) coupled to adigital control circuit, the spectroscopy system having a chargeproportional to energy absorbed from incident radiation subjected to theradiation detector which forms a voltage pulse and a shaped pulse, thesteps of the method comprising: a) providing a pole-zero network coupledalong the shaping amplifier of the spectroscopy system, b) integratingthe shaped pulse and a trailing edge of the shaped pulse in the gatedintegrator for forming a signal having a slope proportional to thepole-zero error in the spectroscopy system, c) converting a first andsecond sample along the slope of the integrated shaped pulse in the ADC,d) comparing values of the first and second sample in the digitalcontrol circuit, e) generating a control signal in response to the firstand second sample value comparison in the digital control circuit, f)applying the control signal generated by the digital control circuit instep e) to the pole-zero network, and g) affecting a change in thepole-zero error in the spectroscopy system by the pole-zero network. 14.The method of correcting pole-zero error in a spectroscopy systemaccording to claim 13, wherein after the step of affecting a change inthe pole-zero error, the method further comprising the steps of: h)determining that a level of pole-zero error in the spectroscopy systemis acceptable, and i) automatically shutting off the pole-zero errorcorrection circuitry.
 15. The method of correcting pole-zero error in aspectroscopy system according to claim 13, wherein a multiplyingdigital-to-analog convertor (MDAC) is employed within the pole-zeronetwork, the MDAC storing a first numeric value taken from a numericvalue range dependent on a bit-value of the MDAC, the MDAC numeric valuerange defining an MDAC minimum and maximum numeric value, a current MDACnumeric value equal to a current DAC numeric value wherein the DACnumeric value is defined as a second numeric value taken from the MDACnumeric value range representing a function of the control signal. 16.The method of correcting pole-zero error in a spectroscopy systemaccording to claim 15, wherein the step of comparing the values of thefirst and second sample comprises the step of determining whether thevalue of the first sample is equal to, less than or greater than thevalue of the second sample.
 17. The method of correcting pole-zero errorin a spectroscopy system according to claim 16, wherein if adetermination is made that the value of the first sample is equal to thevalue of the second sample, the method further comprising the step ofinitiating a stop sub-routine.
 18. The method of correcting pole-zeroerror in a spectroscopy system according to claim 16, wherein if adetermination is made that the value of the first sample is less thanthe value of the second sample, the method further comprising the stepsof: a) establishing a new DAC numeric value by decrementing the currentDAC numeric value if the current DAC numeric value is greater than theMDAC minimum numeric value, and b) updating the current MDAC numericvalue to be equal to the new DAC numeric value.
 19. The method ofcorrecting pole-zero error in a spectroscopy system according to claim16, wherein if a determination is made that the value of the firstsample is greater than the value of the second sample, the methodfurther comprising the steps of: a) establishing a new DAC numeric valueby incrementing the current DAC numeric value if the current DAC numericvalue is less than the MDAC maximum numeric value, and b) updating thecurrent MDAC numeric value to be equal to the new DAC numeric value. 20.The method of correcting pole-zero error in a spectroscopy systemaccording to claim 16, wherein prior to the step of comparing the valuesof the first and second sample, the method further comprising the stepsof: a) setting the current DAC numeric value to the next integer valueup from one-half the MDAC maximum numeric value, and b) setting acurrent adjust numeric value to one-half of the current DAC numericvalue.
 21. The method of correcting pole-zero error in a spectroscopysystem according to claim 20, wherein if a determination is made thatthe value of the first sample is less than the value of the secondsample, the method further comprising the steps of: a) establishing anew DAC numeric value by decrementing the current DAC numeric value bythe current adjust numeric value, b) establishing a new adjust numericvalue by dividing the current adjust numeric value in half if thecurrent adjust numeric value is greater than one, and c) updating thecurrent MDAC numeric value to be equal to the new DAC numeric value. 22.The method of correcting pole-zero error in a spectroscopy systemaccording to claim 20, wherein if a determination is made that the valueof the first sample is greater than the value of the second sample, themethod further comprising the steps of: a) establishing a new DACnumeric value by incrementing the current DAC numeric value by thecurrent adjust numeric value, b) establishing a new adjust numeric valueby dividing the current adjust numeric value in half if the currentadjust numeric value is greater than one, and c) updating the currentMDAC numeric value to be equal to the new DAC numeric value.
 23. Themethod of correcting pole-zero error in a spectroscopy system accordingto claim 15, wherein the step of comparing the values of the first andsecond samples comprises the steps of: a) calculating a differencebetween the second and first sample for a plurality of pulses forrendering a sequence of differences, b) calculating a value S by summingthe sequence of differences, c) calculating a value I by multiplying thevalue S by a predetermined gain constant value ai, d) calculating avalue P by multiplying a most recent difference between the second andfirst sample of the sequence of differences by a predetermined gainconstant ap, e) calculating a value E by summing the value P with thevalue I, and f) comparing the value E with a value B wherein the value Bis a predetermined acceptable error band.
 24. The method of correctingpole-zero error in a spectroscopy system according to claim 23, whereinif a determination is made that the value of E is greater than the valueof B, the method further comprising the steps of: a) establishing a newDAC numeric value by decrementing the current DAC numeric value by thevalue of E, and b) updating the current MDAC numeric value to be equalto the new DAC numeric value.